1. Field of the Invention
The present invention relates to image heating devices for heating toner images formed on recording materials.
Known examples of image heating devices are a fixing device for fixing an unfixed toner image onto a recording material and a gloss enhancing device that heats a toner image fixed on a recording material to enhance the glossiness of the image.
Image heating devices can be used in image forming apparatuses that form toner images on recording materials by electrophotography. An example of such an image forming apparatus is a multifunction apparatus equipped with multiple functions, such as a copier function, a printer function, and a facsimile function.
2. Description of the Related Art
In a known image forming apparatus employing electrophotography, an unfixed toner image is first formed on a recording material, and subsequently, a fixing device equipped in the apparatus is used to heat and apply pressure on this unfixed image so as to fix the image on the recording material.
As an example of a fixing device, Japanese Patent Laid-Open No. 11-231701 discloses a belt fixing device which is advantageous in that the width of a fixing nip portion (i.e. the measure thereof in the conveying direction of recording material) can be increased for speeding up the image forming process.
A belt fixing device is configured such that, when the fixing process is complete, the device switches to a standby mode by moving a pressure belt away from a fixing roller.
This belt fixing device is known to control the pressure belt to keep the pressure belt from deviating from a preset range in its width direction. Specifically, this is achieved by tilting a steering roller that supports the pressure belt so that the pressure belt is slid sideways within the preset range.
As another mechanism, a position restricting mechanism is known, which is equipped with position-restricting ribs located adjacent to the edges of the inner surface of the pressure belt. These position-restricting ribs can be brought into abutment with a flange of the roller that supports the pressure belt, so that the pressure belt can be prevented from deviating from a preset range.
However, these known examples have the following problems.
Specifically, in a case where a recording material is undesirably attached to the pressure belt as a result of a jam occurring in the fixing device, it is possible that the pressure belt becomes deviated from its preset range while the pressure belt is being pulled out in the course of clearing the jam.
Although such deviation can be prevented if the user pulls the recording material off the pressure belt in the moving direction of the pressure belt, there is a high possibility that the deviation may occur if the user tries to remove the recording material slantwise or sideways from the pressure belt.
Such a phenomenon in which the pressure belt deviates from its preset range is not avoidable with the above-mentioned position restricting mechanism.